Radio-telephony.



G. SEIBT.

RADIO-TELEPHONY.

APPLICATION FILED 1120.20. 1907.

Patented Dec. 19, 1911.

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GEOBG SEIBT, OF'BERLIN, GERMANY, ASSIGN OR TO THE AMALGA-MATED RADIO- TELEGRAPH COMPANY, LIMITED, OF LONDON, ENGLAND.

RADIO-TELEPHONY.

Specification of Letters Patent.

Application filed December 20, 1907. Serial No. 407,397.

To all whom it may concern:

Be it known that I, Grotto Senrr, a subject of the Emperor of Germany, residing at 13 Mathieustrasse, Berlin, in the Empire of Germany, have invented certain new and to Radio- Telephony, of which the followlng is a specification. I p

This invention relates to radio-telephony, the chief object being to increase the efficiency of working of radio-telephonic systems.

It is Well known that radio-telephony can be produced by means of electrical oscillations by subjecting the intensity of the oscillations produced by the human voice at the transmitting station to rythmical changes. For this purpose some device is required which will cause either the resistance, the inductance, or the capacity, or any combination of these factors, to vary in accordance with the variations of air pressure which constitute acoustic vibrations. That is to say, the alternate compression and rarefaction of the air must be made to produce corresponding changes' in either the amplitude,

or the periodicity, of the electrical radiations. The simplest form for such an arrangement is to insert a variable resistance, suchas a microphone, directly into the antenna or into a circuitcoupled with the an tenna. By doing so there arises however the disadvantageif microphones'with any kind of resistance are chose'nthat only a very small efficiency can be obtained-by changing the vibrations ofthe air into variations of electrical intensity? According to the present invention the variable resistance is brought into such relation to the fixed resistances that the variation of pressure prodilced'by the acoustic vibrations causes a maximum variation of radiated electrical energy, In the case in which the oscillations are produced in the antenna itself or transferred to it by loose coupling from a closedoscillation circuit, and assuming the microphone to be inserted directly into the oscillation circuit, theory shows that the resistance of the microphone ought to be numerically equal to the other resistances of the antenna, or in other Words, that .the damping'producedby the mlcrophone resistance ought to be the same as the damping prodncedby the resistance 1n the antenna itself. This is shown by the fol lowing consideration of an antenna excited by a loosely coupled closed oscillation circuit:--.Let e represent the E. M. F. induced in the antenna, J the stren th of the cur rent, w, the-resistance of tie microphone, and w the effective alternating current resistance of the antenna. Then, while having resonance, the strength of current is' given by the following equation If the resistance of the microphone is, owing to sound waves falling upon the microphone block or plate, varied by an amount Ato J will be increased or diminished by an amount AJ. The value of AJ is given by'the equation Therefore it can be said that:,-

A m m where K depends upon theintensity ofthe sound but not upon the resistance of the microphone. Substituting this value for Ato the equation becomes m +wmr It is important for radio-telephony that AJ becomes a maximum. Now AJ 1s a maximum or mlnimum when I a I 1,012,e58

By difierentiating Ad with respect to 'LU and equating to zero we obtain 2-- Therefore w=w Also clw and this being a negative quantity shows that the condition w w makes AJ a maximum. Hence the condition for maximum efficiency is that the resistance of the micro-' phone and of the system to which it is connected should be equal.

pacity in parallel with the variable resistance. 'Fig. a shows an inductance in parallel with such variable resistance. Fig. 5 shows capacity and inductance in series with each other and in parallel with the variable resistance. 4

A simple arrangement is shown in Fig. 1 of the accompanying drawings, in which A is the antenna, Ban inductance, C a condenser, D the source of electrical oscillations, and E the microphone; the resistance of this microphone is equal to that of the system to which it is connected. Fig. 2 is similar to Fig. l with the exception that the antenna is inductively coupled to the oscillation circuit by means of the oscillation transformer B B.

If the resistance of the microphone does not satisfy the above stated condition, its

. excess or lack of resistance may be compensated. for; when the microphone has too high a resistance we may connect a condenser F or an inductance G- of determined value in parallel with it as shown in'Figs. 3 and a respectively; the efi'ect of such a shunt circuit being to take part of the cur-- rent and thus compensate for too high a resistance of the microphone alone. When the microphone has too low a resistance, a condenser and an inductance in series may be placed in parallel with it as shown in Fig. 5. The condenser and inductance in series connected across the microphone constitute an oscillatory circuit, which if adjusted out of tune with the received oscillations would tend to damp them, and in this way compensate for too low a resistance of the microphone alone. lhe same'may be done when the microphone, instead of being inserted into the antenna, is inserted into a closed circuit loosely coupled with the an-. tenna as it is in Fig. 2. In the case of a shunt circuit being employed with the microphone, the damping due to the microphone and shunt circuit in combination should be equal to the damping due to the resistance of the rest of the system comprismg the antenna. When the antenna is coupled rigidly to the oscillation-circuit there will be difi'erent relations between the proportion of the resistance of the microphone and the other resistances of the oscillation circuits on account of the circuits affecting each other mutually. But it is always desirable, even if the maximum were not very sharp, to keep the amount of energy consumed by the .microphone equal or nearly equal to the energy spent in the system to whichit is connected.

What I claim and desire to secure by Letters Patent of the United States is 1. In a system of radio-telephony in which the transmitting apparatus comprises means for producing and transmitting electrical oscillations, and means comprising an I 2. In a system of radio-telephony in which the transmitting apparatus comprises means for producing and transmit ting electrical oscillations, and means comprisin 'electrical resistance coiiperating with t e first mentioned means for varying the electrical oscillations b amounts corresponding to variations 0 acoustic vibrations produced by speaking, means contained in a circuit shunted from the said electrical resistance for making the damping efiect of the latter and of the shunt cir cuit incombination equal to that due to the resistance of the system to which they are connected.

In testimony whereof I aflix my signature in presence of two witnesses.

, GEORG SEIBT.

Witnesses:

WoLDn'MAn HAUr'r ARTHUR ScHRoEDnR. 

